Control and motion planning of adaptive hands
The work aims for robust and dexterous grasping and in-hand manipulations using adaptive hands. Adaptive hands are under-actuated and complaint hands which provide robust grasping along with low costs hardware. However, modeling of such hands is a challenging problem due to many uncertainties. Thus, planning and control using standard methods is generally impractical. For that matter, along with extensive hardware design, we incorporate machine learning and advanced planning algorithms to achieve robust manipulations and flexibility in unknown environments.
Sampling-based motion planning for the manipulation of elastic rods
During my post-doctoral research at the University of Illinois (Bretl research group), I investigated sampling-based motion planning approaches for dual arm manipulation for rigid and elastic rods. While the configuration space of a rigid body is given by its pose, the configuration space of a deformable elastic rod is given by its pose and shape. This makes the planning problem of dual-arm manipulation of such elastic rods more complex. However, the configuration space of an elastic rod, i.e., the set of all equilibrium configurations, was shown in previous results to be a six-dimensional smooth manifold. This discovery enables the use of standard sampling-based motion planners to easily plan the manipulation of such rods. We incorporated advanced methods to plan under the constraints (kinematic closure constraint and collisions) while considering efficient computation time.
Dynamic Regrasping by In-Hand Orienting of grasped objects using Non-Dexterous Robotic Grippers
Almost any task on an object requires regrasping of the object prior to performing an intended task by varying between grasp configurations. The human hand uses many methods to perform regrasping manipulations such as in-hand sliding, finger gaiting, juggling, picking and placing, etc. The most complex and inspiring approach is the in-hand orienting dynamic regrasping where an object is released into mid air and regrasped in a different orientation. This manipulation is useful in robotics for rapid manufacturing and reducing the number of robotic arms in production lines. In this work, we present a novel approach for performing in-hand orienting regrasping using computed torque control. To maintain an efficient and low-cost approach, the regrasping is performed using a non-dexterous two-jaw gripper and by utilizing the robotic arm’s dynamics. In addition, we present a novel stochastic motion planning algorithm for performing an optimal manipulation satisfying the kinematic and dynamic constraints. The algorithm optimizes the initial pose of the arm and the control gains. Statistical analysis shows the probability for the algorithm to find a solution if such exists.
In this work the swing-up regrasping problem is presented where an object is manipulated using a robotic arm around a point pinched by the arm’s gripper. The aim of the regrasping is to manipulate the object from an initial angle to regrasp it on a new desired angle relative to the gripper. The pinching point functions as a semi-active joint where the gripper is able to apply only frictional torques on the object to resist its motion. We address the problem by proposing a novel approach. The approach incorporates an impulse-momentum method with an LQR-based controller for stabilization on the desired angle. In particular, a sub-optimal Clipped LQR controller is presented to deal with the dissipative semi-active joint. The interaction of these methods with the unique property of the semi-active joint is investigated and analyzed.
CLIBO: Autonomous climbing robot with claws
A novel robot capable of climbing on vertical and rough surfaces, such as stucco walls. Termed CLIBO (claw inspired robot), the robot can remain in position for a long period of time. Such a capability offers important civilian and military advantages such as surveillance, observation, search and rescue and even for entertainment and games. The robot’s kinematics and motion, is a combination between mimicking a technique commonly used in rock-climbing using four limbs to climb and a method used by cats to climb on trees with their claws. It uses four legs, each with four-degrees-of-freedom (4-DOF) and specially designed claws attached to each leg that enable it to maneuver itself up the wall and to move in any direction. At the tip of each leg is a gripping device made of 12 fishing hooks and aligned in such a way that each hook can move independently on the wall’s surface. This design has the advantage of not requiring a tail-like structure that would press against the surface to balance its weight. A locomotion algorithm was developed to provide the robot with an autonomous capability for climbing along the pre-designed route. The algorithm takes into account the kinematics of the robot and the contact forces applied on the foot pads. In addition, the design provides the robot with the ability to review its gripping strength in order to achieve and maintain a high degree of reliability in its attachment to the wall.
Common grasp search algorithm
This work addresses the problem of designing a simple End Effector for a robotic arm which is able to grasp a given set of objects. The purpose of this work is to develop an algorithm which will find a configuration and design of a universal end-effector for a set of objects. With given a set of all CAD models of the parts, the idea is to design an end-effector that is universal in the sense of being able to hold a wide set of components for multiple manipulation tasks. The algorithm will be able to characterize the objects geometries and find a configuration for grasping them. An optimal configuration is the one which can stably grasp the object even under the application of external wrench due to the task being done, i.e., we require Force-Closure grasp.
The OCOG (Object COmmon Grasp) algorithm developed, searches for a common grasp over the set of objects. The search algorithm maps all possible grasps for each object which satisfy a quality criterion. The mapped grasps are represented by feature vectors in a high-dimensional space. This feature vector describes the shape of the gripper. We generate a database of all possible grasps for each object in the feature vector space. Then we use a search algorithm for intersecting all possible grasps over all parts and finding a common grasp suitable for all objects. The search algorithm utilizes an index structure termed kd-tree for representing the database of the sets of feature vectors. The kd-tree structure enables an efficient and low cost search for common points between the sets. Each point (feature vector) is the grasp configuration for a group of objects, which implies for the future end-effector design. The final step classifies the objects to grasps found, according to the common points found. The algorithm will be useful for assembly line robots in reducing end-effector design and manufacturing time and final product cost.
This work was supported by General Motors Corp. Ltd.